This invention generally relates to a mechanical linkage assembly. More specifically, this invention relates to a self retaining clevis pin which requires no additional retention hardware or installation operations after being pressed into the clevis. The device is adapted for use as a component of an automotive power seat mechanism.
Clevis assemblies are a common mechanical linkage to transmit force and allow pivotal motion between two mechanical members. A typical clevis assembly includes a clevis member having a pair of spaced apart clevis arms with a pin extending between the arms for attachment of a connecting lug between the arms. The arms and lug are commonly drilled with clearance through holes to receive the pin. The cylindrical pin is typically retained by an enlarged head at one end and a mechanical fastener at the other end. Mechanical fasteners such as cotter pins, resilient clips, or threaded nuts are commonly used in the art. U.S. Pat. Nos. 5,286,130, 4,113,397, and 4,932,807, for example, disclose these types of mechanical fasteners and techniques previously known in the art.
Cotter pins, resilient clips, and threaded nuts all require an additional assembly operation beyond inserting the pin in the clevis assembly to secure the pin. In each case the assembly operation requires alignment of the fastener with the pin which can be difficult to achieve, particularly in an automated assembly.
When utilizing a cotter pin, the cotter pin must be inserted in a cross-hole through the clevis pin and the ears extending beyond the clevis pin shaft are then bent to retain the cotter pin.
Resilient fasteners, commonly referred to as e-clips or circlips, require alignment of the clip with an annular groove machined in the clevis pin prior to insertion, which typically requires a special tool. Resilient clips are particularly prone to being plastically deformed and therefore non-functional or springing away if not correctly installed. Incorrect installation can result in clips which fall off or are left within the product possibly causing damage and customer dissatisfaction.
Threaded nuts require costly threading of the clevis pin and are complex to mechanically assemble due to the potential for cross-threading. Since high volume product assembly continues to move toward automation and a reduced number of parts in the assembly is desirable wherever possible, current techniques for securing clevis pins with separate fasteners do not fully optimize the assemblies because the assemblies continue to require additional parts and complex assembly techniques.
One approach to a self retaining pin is taught in U.S. Pat. No. 4,682,687 where a pintle chain is shown with polymer links and a plurality of pins connecting the links. The ""687 patent shows a headless pin with a D-shaped noncircular first end to resist axial rotation when properly aligned and inserted within a corresponding D-shaped hole in the link. Diamond or annular shaped knurling on the second end restrains axial translation. One disadvantage of a self retaining pin which depends on a noncircular shape to resist rotation is that a corresponding noncircular hole must be formed in the mating part. An even more important disadvantage is that the noncircular feature must be properly oriented for assembly which may take additional time and effort for hand assembly and make automated assembly difficult or costly. The diamond or annular shape knurling of the pintle chain pin may be adequate for axial retention of the pin under cyclic tensile loading as found in a chain but could prove inadequate under more complex loading or sequences of loading if used in a clevis application. The present invention provides more positive axial retention and lower insertion forces, for a given interference fit, than diamond or annular knurling due to the angulation of the projections called xe2x80x9cfettersxe2x80x9d toward the head allowing easy insertion and difficult extraction in a manner analogous to the action of a barb on a fish hook.
The present invention is used in an automotive power seat mechanism. Motive power is provided by a motor and leadscrew to a polymer nut. Integral with the nut is a clevis member having a pair of spaced apart clevis arms with the pin of the present invention extending between the arms for attachment of the seat linkage system.
Unrelated to the general background of clevis pin retention, but of interest to the background of the fetters in the present invention are xe2x80x9cChristmas treexe2x80x9d fasteners. These fasteners are typically made of plastic and used for attachment of components to sheet metal. Typically a Christmas tree fastener takes the form of a headed pin with a series of angled disks extending laterally along the longitudinal axis of the pin shaft. The disks are angled back toward the pin head to create a directional bias favoring insertion and resisting retraction. When pushed into holes through layers of material, the disks elastically deflect inward while passing through the hole and return to an open position when completely through the holes thereby resisting retraction of the fastener and attaching the layers of material to one another.
The present invention provides a self retaining pin for a clevis assembly which overcomes the problems and disadvantages of the conventional techniques in the art. The invention also provides a self retaining pin which requires no additional retention hardware or installation operations after being pressed into the clevis.
Briefly, the present invention includes a self retaining elongated pin for use in a clevis. The clevis is fabricated from a material softer than the pin material, such as a polymer material. The pin has a generally cylindrical shaft having one or more shaft diameters with an enlarged head at one end and a generally tapered or radiused end at the other. Knurling is provided on either the shaft or the head to resist axial rotation of the pin. Axial translation of the pin is restrained by the head in a first direction and by the fetters in the opposite direction. The fetters are substantially radially symmetrical features with each fetter having a root and a tip with corresponding root diameter and tip diameter. In the preferred embodiment, the fetter tip diameter is larger than the shaft diameter and is smaller than the head diameter. The fetters, particularly the fetter tips, engage the clevis in an interference fit. The fetters are angled such that the fetter tip is directed toward the head to preferentially favor insertion and resist removal of the pin.